Fusible element electric cut-outs.



R. C. COLE.

FUSIBLE ELEMENT FOR ELECTRIC CUT-OUTS.

APPLICATION FILED JULYZQ, 1915.

Patented Apr. 25,1916.

THE COLUMBIA PLANOGRAPH c0, WASHINGTON. D. c.

"UNITED STATES PATEN T OFFICE.

ROBERT C. COLE, OF HARTFORD, CONNECTICUT, ASSIGNOR TO THE JOHNS-PRATT COMPANY, OF HARTFORD, CONNECTICUT, A CORPORATION OF CONNECTICUT.

EUSITBLE ELEMENT FOR ELECTRIC CUT-OUTS.

Specification of Letters Patent.

Patented Apr. 25, 1916.

To all whom it may concern Be it known that 1, ROBERT C. Gone, a citizen of the United States, residing at Hartford, in the county of Hartford and State of Connecticut, have invented a new and useful Improvement in Fusible Elements for Electric Cut-Outs, of which the following is a specification.

This invention relates to those elements which form the fusible links of inclosed fuses containing solid, liquid or gaseous in sulating mediums.

The object of the invention is to provide a simple method for concentrating the heat and insuring the break of the link at the desired locality, and calibrating the link so that it will open the circuit at the predetermined moment after the current flow has reached the maximum limit, with great exactness and without weakening the link.

The invention can be advantageously employed in making links for low voltage fuses, but it is particularly useful in connection with the making of the fusible elements of high voltage fuses which have links formed ofone or more very thin fusible strips or ribbons, such for example as the strips of 2,300 volt fuses, which in some cases for fuses approximating 20 amperes have been made 6 inches long, .15 inches wide and .0025 inches thick. It has been common practice to notch or to perforate fuse strips for the purpose of calibration and localizing the break. This method, however, materially weakens the strips, and is particularly objectionable when the strips are very thin and narrow, and consequently delicate, and where they are carried by supports which have considerable expansion when heated, the expansion of the supports frequently tearing apart the strips where they are weakened by a reduction in area due to the calibration notches or perform tions.

I have discovered that the desired heat concentration for localizing the break and the required calibration for insuring exactness in operation, can, without in the least weakening the strips, be obtained by folding sections of the strips on themselves and thus reducing the superficial area at the desired localities intermediate the ends of the strips with the consequent reduction of the radiating surface in contact with the surrounding insulating medium necessary to attain the required result.

In the accompanying drawings Figure 1 illustrates a multiple strip link formed according to this invention. Fig. 2 is a cross section on the plane indicated by the dotted line 2-2 on Fig. 1. Fig. 3 shows on greatly enlarged scale a plan of a portion of a link formed according to this invention. Fig. elshows a side view of the same. Fig. 5 is a cross section through the folded portion of the link with a fine wire clip applied so as to keep the bent portion from unfolding.

In the embodiment of the invention illustinted there are two metallic terminals 1 desirably formed of copper wire or other metal having sufiicient conductivity to carry the current. On the inner ends of these terminals are metallic disks 2. A glass rod 3 separates and holds in the desired relative positions the terminals and disks. Connecting the disks and with their ends in electrical contact with the peripheries thereof, in the form shown, are four conducting strips 4. These strips are desirably made of Zinc, but may be of other suitable conducting material, and in structures which have been made in accordance with this invention they are from .001 to .0025 inches thick according to the capacity of the fuse to be produced. Under the commonly practised method of notching or perforating for calibration, such delicate strips, owing to the expansion of the glass and due to the mechanical problems incident to the manu facture of fuses in large numbers, and also to the rough usage they are liable to be subjected to during transportation and when put to use, were frequently torn apart and ruptured at the weakened portion. In order to remedy this defect I have folded together sections of the strips, as at 5, so as to reduce at that point the superficial area in contact with the insulatin medium with which the element is surrounded when inclosed in a fuse casing, and have discovered that by this means the desired localization of rupture and the required calibration for exactness in time of opening can be obtained without in any way reducing the tensile strength of the strips. It has been found advantageous to apply spring clips 6 of fine wire over the bent portions, or the portions of the strips folded together so as to keep them from unfolding.

The invention, as indicated, is applicable to fusible strips of any size Which it is desirable to calibrate, and to links-of one or any number of strips. To attain the object desired the strips may be folded at one or any number of places along their lengths.

The invention claimed is:

1. A fuse element consisting of a thin strip of fusible metal of uniform cross sectional area with a portion that is intermediate the terminals folded on itselfso as to reduce the superficial radiating surface at the folded point.

2. A fuse element consisting of a thin strip of fusible metal With a portion that is intermediate the terminals of the strip folded on itself so as to reduce the superficial area of the strip Where folded, and a clip appliedrto the folded portion for holding it together.

3. A fuse element comprising conducting terminals, and a plural number of thin fusible metal strips of uniform cross sectional area, With portions between the terminals folded onthemselves to reduce the superficial area and radiating surface at the desired localities, connecting-the terminals.

ROBERT C. COLE. Witnesses:

HAZEL G. BRAINARD, D NCAN C. HOOKER.

copies Ofrthi-S patent may be obtained tor fivecents each, by addressing-the Commissioner of Patents, Washington, D. G. 

